[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 290234
TCDAT3

Hurricane Sam Discussion Number  26
NWS National Hurricane Center Miami FL       AL182021
1100 PM AST Tue Sep 28 2021

Satellite images suggest that Sam has strengthened.  The eyewall of
the hurricane has become more intense, with a warmer eye noted
during the past several hours since the last reconnaissance aircraft
departed.  The initial wind speed is nudged upward to 120 kt, a
little above what the previous aircraft mission from this afternoon
supported.  Another Air Force Reserve Hurricane Hunter plane is
scheduled to fly through Sam in a few hours for a better look at the
intensity.

Sam is forecast to move into an area with somewhat lower wind shear
and higher ocean heat content by late Wednesday.  In addition, the
hurricane will likely be moving a little faster, which decreases the
upwelling potential under the storm.  These factors lead me to
believe Sam isn't quite done intensifying, and could reach another
peak sometime late Wednesday or Thursday.  The one fly-in-the-
ointment to this forecast is another eyewall replacement cycle
potentially beginning, although recent microwave data doesn't give
that impression.  Thus, the new forecast is raised from the last
one during the first couple of days, on the higher side of the
guidance.  A more consistent weakening trend is expected late week,
due to cooler SSTs and increasing shear, and no significant
changes were made to the official forecast at long range.

The hurricane continues moving northwestward at about 8 kt.  Models
are locked into this track continuing for the next day or two at a
faster pace around the southwestern portion of a strengthening
Atlantic subtropical ridge.  Thereafter, Sam should turn northward
on Friday and northeastward this weekend, likely a fair distance
east of Bermuda, due to a large mid-latitude trough moving off of
the United States east coast.  Model guidance remains in close
agreement on almost all of the forecast, and the only significant
change from the last advisory is an eastward adjustment on Day 5 due
to guidance suggesting that Sam gets shunted more eastward by the
trough, rather than captured by it.


Key Messages:

1. Large swells generated by Sam are affecting the Leeward Islands
and will spread to portions of the Virgin Islands, Puerto Rico,
Hispaniola, the Bahamas, and Bermuda by Thursday or Friday.
Significant swells will likely reach the east coast of the United
States and Atlantic Canada by the weekend.  These swells will likely
cause life-threatening surf and rip current conditions, and
beachgoers and other interests along these coasts are urged to
follow the advice of lifeguards and local officials through the
upcoming weekend.


FORECAST POSITIONS AND MAX WINDS

INIT  29/0300Z 18.4N  55.6W  120 KT 140 MPH
 12H  29/1200Z 19.1N  56.7W  120 KT 140 MPH
 24H  30/0000Z 20.2N  58.2W  125 KT 145 MPH
 36H  30/1200Z 21.8N  59.9W  125 KT 145 MPH
 48H  01/0000Z 23.9N  61.2W  120 KT 140 MPH
 60H  01/1200Z 26.4N  61.9W  115 KT 130 MPH
 72H  02/0000Z 29.1N  61.8W  110 KT 125 MPH
 96H  03/0000Z 35.0N  58.0W  100 KT 115 MPH
120H  04/0000Z 40.0N  52.0W   85 KT 100 MPH

$$
Forecaster Blake
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